TABLE 2

Effect of extracellular pH on the uptake of various compounds by OATP-B

Uptake of [3H]E13S, [3H]DHEAS, fexofenadine, and [3H]TCA were measured for 1, 5, 30, and 2 min, respectively, and other compounds were measured for 10 min. Concentration used for each test compound was shown in the respective parenthesis. OATP-B-specific was obtained by subtracting the uptake by mock-transfected cells from the OATP-B cDNA-transfected cells. Each value represents the mean ± S.E.M. (n = 3 or 4). For the uptake of [3H]TCA, the uptake medium including 0.5% BSA was used to decrease the nonspecific binding.

Test Compounds
Uptake
pH 7.4
pH 5.0
Mock
OATP-B
OATP-B-specific
Mock
OATP-B
OATP-B-specific
μl/mg protein
[14C]Acetic acid (4.94 μM) 15.5 ± 0.41 18.3 ± 1.00 2.81 ± 1.00 77.2 ± 2.04 81.7 ± 5.63 4.50 ± 5.63
[3H]DHEAS (2.98 nM) 138 ± 5.55 214 ± 5.19* 76.4 ± 5.19 230 ± 3.43 443 ± 2.63* 213 ± 2.63
[3H]E13S (5.43 nM) 141 ± 5.59 237 ± 6.78* 96.0 ± 6.78 173 ± 3.34 483 ± 3.67* 310 ± 3.67
[3H]E217βG (5.72 nM) 39.2 ± 2.01 38.5 ± 1.81 -0.68 ± 1.81 53.3 ± 1.86 58.6 ± 1.93 5.31 ± 1.93
Fexofenadine (10 μM) 51.7 ± 1.07 58.5 ± 1.00* 6.82 ± 1.00 117 ± 3.79 140 ± 2.66* 23.7 ± 2.66
[14C]Lactic acid (1.91 μM) 9.41 ± 0.82 10.3 ± 0.93 0.84 ± 0.93 119 ± 1.93 120 ± 1.66 1.17 ± 1.66
[14C]Pravastatin (14.7 μM) 3.99 ± 0.37 4.44 ± 0.46 0.44 ± 0.46 72.1 ± 1.33 92.4 ± 1.86* 20.3 ± 1.86
[3H]TCA (0.15 μM)
32.5 ± 1.06
35.4 ± 1.28
3.28 ± 1.28
40.4 ± 1.04
53.5 ± 1.35*
13.1 ± 1.35

  • DHEAS, dehydroepiandrosterone sulfate; E13S, estrone-3-sulfate; E217βG, estradiol-17β-glucuronide; TCA, taurocholic acid.

    OATP-B-cDNA-transfected or mock cells were preloaded for 20 min at 37°C in the incubation medium (pH 7.4).

  • ↵* indicates a significant difference from the uptake of mock-transfected cells (p < 0.05).